Inkjet recording is known to be a superior recording method that can be applied to a comparatively wide range of recorded materials, and research and development is being actively carried out on recording apparatuses, recording methods, recording materials and the like. At present, ink used for inkjet recording consists mainly of dye ink that uses a dye for the colorant.
On the other hand, the most common type of inkjet recording media is provided with an ink absorbing layer having voids for incorporating ink on a base material, while also being provided with a porous glossy layer as necessary. This type of paper was designed with the emphasis of being compatible with currently popular dye ink, and is already widely used in the form of special-purpose inkjet paper, and particularly glossy paper. Although the use of this paper allows the obtaining of extremely high-definition images having superior glossiness, since the raw materials are extremely expensive while also requiring a complex manufacturing process, the production cost is extremely high as compared with general commercial printing gloss-coated paper. Consequently, the applications thereof tend to be limited to cases requiring the output of photographs or other high-quality output, while being difficult to use in commercial printing fields requiring inexpensive, large-volume output such as leaflets, catalogs and pamphlets.
In addition, with regard to the design concept of the resulting image with respect to long-term storage, since the dye itself has low resistance to ultraviolet light and ozone, the most common approach has been to ensure image shelf life by incorporating the dye as deep as possible in the ink receiving layer of the inkjet recording media to block the effects of the atmosphere and ultraviolet light as much as possible, while also protecting the dye with antioxidants and stabilizers added in advance to the ink receiving layer. Consequently, it is necessary to use a large amount of ink having a decreased concentration of colorant, thereby resulting in increased printing costs. In addition, there have also been problems such as decreased image quality due to bleeding when printing on ordinary paper.
In order to solve such problems, pigment inks that use pigment for the colorant have been proposed in recent years for use as inkjet recording ink. Although this pigment ink has superior image density, water resistance and weather resistance in comparison with dye inks and allows the obtaining of images with little bleeding, since coloring and glossiness are inadequate or considerable time is required for the ink to dry after printing when printing on recording media having a coating layer, these inks had problems such as inferior image fixability.
In order to solve such problems, Patent Literature 1 describes a recording liquid containing a pigment having a particle diameter of 40 nm to 100 nm and a urethane-based resin having superior glossiness, blackness and rubfastness on special-purpose photo quality paper. However, the recording media of the present invention uses inexpensively available, general gloss-coated paper for commercial printing, and does not include special-purpose photo quality paper.
Patent Literature 2 describes superior glossiness, image density, drying and fixability on glossy media by defining the contents of a self-dispersing pigment and resin fine particles. However, if the average particle diameter of the pigment is within the range of 200 nm or less, and particularly in the case of using the pigment having an average particle diameter near 200 nm, the pigment solidifies in the vicinity of the inkjet nozzle thereby resulting in increased susceptibility to the occurrence of defective discharge.
Patent Literature 3 describes superior glossiness and rubfastness of color images on glossy media with a recording liquid containing carbon black and a dispersant in the form of an anionic group-containing styrene-acrylic copolymer. However, since the defined physical values of the media are gloss value and haze value, and the glossy media is special-purpose inkjet paper, there is the potential for the glossiness and rubfastness of color images to be inadequate when printed on the recording media of the present invention.
Carbon black having comparatively low DBP oil absorption, namely low structure carbon black, allows the obtaining of glossy images as a result of orienting comparatively smoothly on paper. For example, although the carbon blacks used in Patent Literature 4 and Patent Literature 5 have comparatively low DBP oil absorption levels allowing the obtaining of high gloss on glossy media, they have the shortcoming of inadequate image density.
Patent Literature 6 and Patent Literature 7 describe superior gloss or rubfastness on special-purpose inkjet paper such as photo paper with a recording liquid containing an aqueous dispersion of water-insoluble vinyl polymer particles containing carbon black. However, the recording ink used in these publications consists primarily of that for printing on ordinary paper, while as was previously described, the recording media of the present invention uses inexpensively available, general gloss-coated paper for commercial printing, and does not include special-purpose glossy or photo quality paper.
Patent Literature 8 describes the use of a colorant containing a self-dispersing pigment or polymer as an inkjet recording method allowing the obtaining of adequate image density regardless of the media, such as ordinary paper or glossy media. Although a more composite black color is obtained than inks mainly using a colorant containing a polymer other than a black polymer in the case the medium is a glossy medium, this differs from a method for obtaining a recorded matter having superior image density and glossiness with black ink as is targeted by the present invention, and does not allow the obtaining of a black color of the composite black having adequate image density and glossiness.
Patent Literature 9 describes an inkjet recording method for printing using a suitable ink corresponding to the type of media such as ordinary paper or glossy media, wherein two black ink nozzles for respectively discharging two different types of black ink are provided on a printing head, and by printing by discharging from the second nozzle a black ink that uses a colorant containing a resin-coated pigment when printing on glossy media, glossy media printed images are obtained having superior fixability. However, since the resin-coated pigment is not specifically defined, there is the potential for being unable to obtain adequate image density and glossiness in the case of mixing in a pigment having a somewhat large particle diameter, for example, as well as the occurrence of problems such as defective discharge due to the pigment solidifying in the vicinity of the inkjet nozzle.
Patent Literature 10 describes an inkjet recording ink containing a self-dispersing carbon black, adsorbed with a water-dispersible high molecular weight compound and which does not pass through a gel filtration chromatography column, and water, wherein the water-dispersible high molecular weight compound has a gel permeation chromatography permeation rate of 20% or less when in a free state from the carbon black. In addition, this publication also discloses to the effect that, although paper recording media is classified into “ordinary paper” and “special-purpose gloss-coated paper”, the latter “special-purpose gloss-coated paper” is further classified into “semi-glossy paper” and “glossy paper”, this ink can particularly form glossy recorded images on media in the form of “ordinary paper” other than the “special-purpose gloss-coated paper”.
Patent Literature 11 describes a composite black ink composing a color printing ink set, wherein the composite black ink is provided with an ink composition (A) containing a self-dispersing carbon black, and an ink composition (B) containing ordinary carbon black and a resin emulsion at 20 times or more the amount of the ordinary carbon black, rub resistance with respect to glossy paper having high planar smoothness being satisfied by the ink composition (A), and coloring and image density being satisfied by the ink composition (B).
Patent Literature 12 describes a recording ink containing an acidic carbon having a low pH and a basic carbon having a high pH, and that a high print density is achieved due to the acidic carbon while ease of nozzle discharge and storage stability are achieved due to the basic carbon.
Patent Literature 13 describes an inkjet recording ink containing dye-colored, water-insoluble aryl (meth)acrylate fine particles having a thiomethyl group on the end of the main chain thereof in an aqueous medium, and that this ink allows to obtain recorded matters having superior print density when printed on ordinary paper and to obtain recorded matters having superior glossiness when printed on glossy paper. Patent Literature 14 describes a black ink that similarly uses the water-insoluble aryl (meth)acrylate and carbon black having a large specific surface are and high DBP oil absorption.
Patent Literature 15 describes an inkjet recording ink that combines the use of a carbon black having a large specific surface area and high DBP oil absorption (highly structured carbon black) and a carbon black having a small specific surface area and low DBP oil absorption (lowly structured carbon black), and that although the former highly structured carbon black is suitable for enhancing OD density of images printed on ordinary paper, the latter lowly structured carbon black compensates for insufficient glossiness, surface roughness and insufficient durability of images printed on glossy paper by the former.
Patent Literature 16 describes that in the case of using two types of ink according to differences in recording media and in the case the recording media is coated paper, printing is carried out with a carbon black pigment ink in the case of printing on ordinary paper with black ink containing a dye.
Patent Literature 17 describes inkjet printing composed of an ink set of an aqueous pigment ink composition (1) and an aqueous clear ink (2) containing only polymer fine particles but not a colorant, wherein the ink set (1) uses a set composed of three members consisting of a thin black ink having a low carbon black concentration (11), a gray-to-gray black ink having an intermediate carbon black concentration (12), and thick black ink having a high carbon black concentration (13).
The use of a plurality of types of ink or the use of a plurality of types of colorants as in Patent Literatures 9 to 17 clearly has various problems.
In this manner, it was difficult to obtain a recorded matter having superior image density and glossiness on a recording media targeted by the present invention as well as high image quality approaching that of commercial printing such as web offset printing.
[Patent Literature]
[Patent Literature 1] Japanese Patent Application Laid-Open (JP-A) No. 2004-285344
[Patent Literature 2] JP-A No. 2004-35716
[Patent Literature 3] JP-A No. 2005-336438
[Patent Literature 4] JP-A No. 2001-348523
[Patent Literature 5] JP-A No. 2002-97390
[Patent Literature 6] JP-A No. 2003-231831
[Patent Literature 7] JP-A No. 2005-42098
[Patent Literature 8] JP-A No. 2002-327138
[Patent Literature 9] JP-A No. 2004-25545
[Patent Literature 10] JP-A No. 2005-163017
[Patent Literature 11] JP-A No. 2005-264115
[Patent Literature 12] JP-A No. 2006-111691
[Patent Literature 13] JP-A No. 2006-176686
[Patent Literature 14] JP-A No. 2005-42005
[Patent Literature 15] JP-A No. 2005-307207
[Patent Literature 16] JP-A No. 11-1647
[Patent Literature 17] JP-A No. 2005-52984